Implantable electrical medical devices, such as cardiac pacemakers, defibrillators, and neurostimulators, are intricately designed electrical devices used to regulate certain medical conditions. These devices are either permanently implanted into the human body, or are implanted and remain there for an extended period of time (typically many years). They must be able to withstand the harsh environmental conditions of the human body, and must be operable for a very long period of time without needing repair or replacement. Because they generate electrical signals, special considerations are taken into account when designing the circuitry, so as to maintain the integrity of the electrical connections between the power source, the electrodes, and the organ to which they are attached.
Conventional pacemakers, for example, are essentially comprised of two parts: the pacemaker “chamber” and the electrical leads. The chamber contains the power source (typically a battery), the circuitry that detects electrical signals emanating from the heart and returns electrical signals to the heart, and a timing device to regulate the patient's heartbeat. The leads are the conducting wires that carry the electrical signal from the chamber to the heart. Current pacemaker leads are typically platinum wires, having one end connected to the patient's heart and the other end connected to the circuitry in the pacemaker chamber. The wire is fed through a ceramic insulating substrate, for example an alumina-based substrate, within the chamber, and the connection site is then brazed with gold to create a hermetic seal.
U.S. Patent Publication Nos. 2013/0110212 and 2013/0109986 disclose a pacemaker assembly. The assembly includes a lead wire structure, which is attached at one end to a pulse generator and at the other end to an electrode head (which is ultimately attached to a human organ). The lead wire structure includes at least one sub-lead wire. The sub-lead wire includes a core wire, around which a carbon nanotube composite wire is wound. It is the core wire which conducts signals from the pulse generator to the human organ. According to at least one embodiment, the sub-lead core wire is formed of platinum.
Typically, the prior art devices require long manufacturing processing times and do not allow for easy changes to the configuration of the device during production. The structure of the leads and their connection to the ceramic substrate add to these disadvantages. Replacing the leads with a material that takes up less space than a solid wire would also allow these devices to be more compact, thus more efficient and comfortable for the patient. Lastly, as gaps are inevitably formed at the junction of the platinum wire and the ceramic substrate, gold brazing is required to form a hermetic seal. Not only is gold an expensive precious metal, but this brazing process requires an extra manufacturing step.
There is, therefore, a need for a conductive material which can replace the leads in implantable medical devices, while maintaining the requisite electrical properties, hermetic properties, and the ability to withstand the bodily environment without contaminating it.